8o COMPARATIVE PHYSIOLOGY OF THE BRAIN 



explanation for this behaviour is that they crawl about 

 in the dish during the night and in the morning stop 

 in the darkest place. These animals have at their 

 oral pole not only a brain but also comparatively well- 

 developed eyes. I resolved to try whether a decapit- 

 ated Planarian, in spite of the loss of brain and eyes, 

 would still show the same reactions toward light as 

 the normal animals. This is the case to a most sur- 

 prising extent. In the evening, about sixty specimens 

 of Planaria torva were cut transversely just behind 

 the brain and eyes. All the pieces were put into a 

 dish with vertical sides which was half covered with 

 black paper. The next morning nearly all the pieces, 

 posterior as well as anterior, were found in the covered 

 portion of the aquarium, where they were scattered 

 about pretty uniformly. In the uncovered portion of 

 the dish I found a few pieces, anterior, however, as 

 well as posterior ones, crowded together in a corner 

 where the intensity of the light was a comparative 

 minimum. Upon repeating this experiment with nor- 

 mal Planarians, the same result was obtained. When 

 the decapitated animals were at rest in the covered 

 portion of the dish, their rest was soon disturbed if, 

 without jarring the aquarium, the dark paper was 

 removed suddenly. At first they crawled about on 

 the side away from the light, then they collected 

 again where the intensity of light was a relative mini- 

 mum. This reaction occurred just as in normal ani- 

 mals, except that the reaction-time of the brainless 

 animals was greater than in normal animals. In the 



